It is desirable to enable mobile devices which are typically connected to a mobile network to also directly communicate with each other, i.e., via so-termed device-to-device (D2D) communication.
D2D communication is characterized by a direct wireless communication path between two mobile terminals, such as the mobile devices, while maintaining, at least at some moments in time, at least a signaling connection with/via a base station of the wireless communication network, i.e., of the mobile network. The direct wireless communication path between mobile terminals allows to offload the base station(s), the access network and the core network of the wireless communication network from most of the data and signaling exchanged between the mobile terminals. The signaling connection with (a base station of) the wireless communication network allows the wireless communication network to control the resources assigned to the direct communication path between the terminals.
A mobile device which, at a given time, uses D2D communication instead of communicating via the mobile network may be referred to as operating in Direct Mode Operation (DMO). DMO offers advantages such as, e.g., enabling mobile communication between users outside a range of the mobile network, reducing of load from the base stations and/or from the core nodes of the mobile network, etc.
An example of a mobile communication standard which enables mobile communication between mobile devices both via the mobile network as well as via the aforementioned D2D communication is Terrestrial Trunked Radio (TETRA).
Another example of such a mobile communication standard is Global System for Mobile Communications (GSM). The GSM standard includes a so-termed local call, local switch feature in which mobile communication between mobile devices which are connected to a same base station of the mobile network is not routed through the core nodes of the mobile network, but rather directly from the base station to each respective mobile device.
Yet another example is Long Term Evolution (LTE). Recent developments in LTE include D2D communication between mobile devices. It is noted that in the context of LTE, such D2D communication is also referred to as Direct LTE.